The present invention relates to an inductive coupling data transmission device, comprising an inductive antenna circuit driven by an antenna signal and a control circuit comprising binary ports that can be set to high impedance and that have a non-zero internal resistor.
In particular, the present invention relates to devices designed to exchange data with portable electronic objects comprising a contactless integrated circuit, such as contactless smart card readers, electronic label scanners, electronic badge scanners, . . .
According to draft standards ISO 14443-2/A or 14443-2/B, hereinafter referred to as xe2x80x9cISO/Axe2x80x9d and xe2x80x9cISO/Bxe2x80x9d, the antenna coil of a contactless integrated circuit reader is driven by an antenna signal oscillating at a frequency of 13.56 MHz. The data transmission to the integrated circuit is carried out by modulating the amplitude of the antenna signal, with a modulation depth of 100% in the case of standard ISO/A or 10% in the case of standard ISO/B.
FIG. 1 represents a classical data transmission device 1 comprising a microprocessor 2, an oscillator 3, a modulation transistor 4 and a resonant-type antenna circuit 10. The antenna circuit 10 comprises an antenna coil 11 in parallel with a capacitor 12 and receives a direct supply voltage VDD through an inductor 13 and an insulation capacitor 14. The modulation transistor 4 is connected to the terminals of the coil 11 by means of the insulation capacitor 14. The oscillator 3 delivers a signal S1 oscillating at 13.56 MHz and the microprocessor 2 delivers an amplitude modulation binary signal S2 to a port P1. Signals S1 and S2 are applied to an AND gate 5 the output of which delivers a modulation signal S3 applied to the gate of transistor 4, which is shown in FIG. 1. The antenna signal Sa passing through the coil 11 is the image of signal S3.
The advantage of this data transmission device is that the structure is relatively simple but it only allows the amplitude of the antenna signal to be modulated at 100% (ISO/A). To obtain a 10% modulation of the antenna signal Sa (ISO/B), the device becomes more complex and other elements must be added to it.
The device becomes even more complex if it is to be compatible with standards ISO/A and ISO/B so as to be able to transmit data to two different types of integrated circuits. In this case, as shown by FIG. 2, the modulation switch 4 is replaced by a modulation circuit 9 represented in block form. The modulation circuit 9 receives signals S1, S2 and a signal SAB delivered by a port P2 of the microprocessor, allowing the type of modulation required to be selected. To achieve this modulation circuit 9 various electric and/or electronic components are required.
Therefore, one object of the present invention is to provide a data transmission device of the type described above that can modulate the antenna signal with a modulation depth of less than 100% while being simple in structure and inexpensive to produce.
One more particular object of the present invention is to provide a data transmission device that can be multi-purpose and that can modulate the antenna signal with several modulation depths, particularly modulation depths of 10% and 100%.
The present invention also relates to receiving data sent by a contactless integrated circuit by the charge modulation method. In this case, the coil 11 of the data transmission device described above receives a charge modulation signal by inductive coupling, that is mixed with the antenna signal Sa. The charge modulation signal must be extracted from the antenna signal Sa and demodulated by adequate filtering before being decoded. Known demodulation and filtering systems are inconvenient in that they are complex if they are to be compatible with several charge modulation protocols, particularly those stipulated by standards ISO/A and ISO/B.
Thus, another object of the present invention is to provide a demodulation device that is compatible with several charge modulation protocols, while being simple in structure and inexpensive to produce.
To achieve these objects, the present invention provides a method for modulating the amplitude of the antenna signal of an inductive antenna circuit comprising a coil, by means of a control circuit comprising binary ports that can be set to high impedance state and with a non-zero internal resistor, a method in which the antenna circuit is electrically powered by at least two ports of the control circuit, and comprising the steps of: setting the ports providing the electric supply of the antenna circuit to xe2x80x9c1xe2x80x9d, to supply the antenna circuit at full power level, and changing the state of at least one of the ports providing the electric supply of the antenna circuit, to modulate the amplitude of the antenna signal.
According to one embodiment, the ports providing the electric power supply of the antenna circuit are set to xe2x80x9c0xe2x80x9d for a 100% modulation of the antenna signal.
According to one embodiment, at least one port is set to high impedance state while the other port or ports are maintained on xe2x80x9c1xe2x80x9d for a modulation of the antenna signal amplitude of less than 100%.
According to one embodiment, the antenna signal is also modulated in frequency by switch means connected to the terminals of the coil and controlled by an alternative signal.
The present invention also relates to an inductive coupling data sending device, comprising an inductive-type antenna circuit comprising a coil through which an antenna signal passes, a control circuit of the antenna circuit comprising binary ports that can be set to high impedance and with a non-zero internal resistor, in which the antenna circuit is electrically powered by at least two ports of the control circuit, and the control circuit is arranged to modulate the amplitude of the antenna signal in compliance with the method of the present invention.
According to one embodiment, the device comprises an oscillator delivering an alternative signal and switch means controlled by the alternative signal, arranged at the terminals of the antenna coil to modulate the frequency of the antenna signal.
The present invention also relates to a data send/receive device of the type described above, comprising a band-pass filter and a low-pass filter arranged to receive a charge modulation signal present in the antenna signal on a first terminal, and each connected by their other terminal to a port of the control circuit.